// (C) Copyright 2015 Moodle Pty Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import { BehaviorSubject } from 'rxjs';

import { CoreQuestionHelper } from '@features/question/services/question-helper';
import { CoreQuestionsAnswers } from '@features/question/services/question';
import { CoreLogger } from '@singletons/logger';
import { AddonModQuizConnectionErrorComponent } from '../components/connection-error/connection-error';
import { AddonModQuiz, AddonModQuizAttemptWSData, AddonModQuizQuizWSData } from '../services/quiz';
import { CoreDomUtils } from '@services/utils/dom';

/**
 * Class to support auto-save in quiz. Every certain seconds, it will check if there are changes in the current page answers
 * and, if so, it will save them automatically.
 */
export class AddonModQuizAutoSave {

    protected readonly CHECK_CHANGES_INTERVAL = 5000;

    protected logger: CoreLogger;
    protected checkChangesInterval?: number; // Interval to check if there are changes in the answers.
    protected loadPreviousAnswersTimeout?: number; // Timeout to load previous answers.
    protected autoSaveTimeout?: number; // Timeout to auto-save the answers.
    protected popover?: HTMLIonPopoverElement; // Popover to display there's been an error.
    protected popoverShown = false; // Whether the popover is shown.
    protected previousAnswers?: CoreQuestionsAnswers; // The previous answers, to check if answers have changed.
    protected errorObservable: BehaviorSubject<boolean>; // An observable to notify if there's been an error.

    /**
     * Constructor.
     *
     * @param formName Name of the form where the answers are stored.
     * @param buttonSelector Selector to find the button to show the connection error.
     */
    constructor(
        protected formName: string,
        protected buttonSelector: string,
    ) {
        this.logger = CoreLogger.getInstance('AddonModQuizAutoSave');

        // Create the observable to notify if an error happened.
        this.errorObservable = new BehaviorSubject<boolean>(false);
    }

    /**
     * Cancel a pending auto save.
     */
    cancelAutoSave(): void {
        clearTimeout(this.autoSaveTimeout);
        this.autoSaveTimeout = undefined;
    }

    /**
     * Check if the answers have changed in a page.
     *
     * @param quiz Quiz.
     * @param attempt Attempt.
     * @param preflightData Preflight data.
     * @param offline Whether the quiz is being attempted in offline mode.
     */
    checkChanges(
        quiz: AddonModQuizQuizWSData,
        attempt: AddonModQuizAttemptWSData,
        preflightData: Record<string, string>,
        offline?: boolean,
    ): void {
        if (this.autoSaveTimeout) {
            // We already have an auto save pending, no need to check changes.
            return;
        }

        const answers = this.getAnswers();

        if (!this.previousAnswers) {
            // Previous answers isn't set, set it now.
            this.previousAnswers = answers;

            return;
        }

        // Check if answers have changed.
        let equal = true;

        for (const name in answers) {
            if (this.previousAnswers[name] != answers[name]) {
                equal = false;
                break;
            }
        }

        if (!equal) {
            this.setAutoSaveTimer(quiz, attempt, preflightData, offline);
        }

        this.previousAnswers = answers;
    }

    /**
     * Get answers from a form.
     *
     * @returns Answers.
     */
    protected getAnswers(): CoreQuestionsAnswers {
        return CoreQuestionHelper.getAnswersFromForm(document.forms[this.formName]);
    }

    /**
     * Hide the auto save error.
     */
    hideAutoSaveError(): void {
        this.errorObservable.next(false);
        this.popover?.dismiss();
    }

    /**
     * Returns an observable that will notify when an error happens or stops.
     * It will send true when there's an error, and false when the error has been ammended.
     *
     * @returns Observable.
     */
    onError(): BehaviorSubject<boolean> {
        return this.errorObservable;
    }

    /**
     * Schedule an auto save process if it's not scheduled already.
     *
     * @param quiz Quiz.
     * @param attempt Attempt.
     * @param preflightData Preflight data.
     * @param offline Whether the quiz is being attempted in offline mode.
     */
    setAutoSaveTimer(
        quiz: AddonModQuizQuizWSData,
        attempt: AddonModQuizAttemptWSData,
        preflightData: Record<string, string>,
        offline?: boolean,
    ): void {
        // Don't schedule if already shceduled or quiz is almost closed.
        if (!quiz.autosaveperiod || this.autoSaveTimeout || AddonModQuiz.isAttemptTimeNearlyOver(quiz, attempt)) {
            return;
        }

        // Schedule save.
        this.autoSaveTimeout = window.setTimeout(async () => {
            const answers = this.getAnswers();
            this.cancelAutoSave();
            this.previousAnswers = answers; // Update previous answers to match what we're sending to the server.

            try {
                await AddonModQuiz.saveAttempt(quiz, attempt, answers, preflightData, offline);

                // Save successful, we can hide the connection error if it was shown.
                this.hideAutoSaveError();
            } catch (error) {
                // Error auto-saving. Show error and set timer again.
                this.logger.warn('Error auto-saving data.', error);

                // If there was no error already, show the error message.
                if (!this.errorObservable.getValue()) {
                    this.errorObservable.next(true);
                    this.showAutoSaveError();
                }

                // Try again.
                this.setAutoSaveTimer(quiz, attempt, preflightData, offline);
            }
        }, quiz.autosaveperiod * 1000);
    }

    /**
     * Show an error popover due to an auto save error.
     */
    async showAutoSaveError(ev?: Event): Promise<void> {
        // Don't show popover if it was already shown.
        if (this.popoverShown) {
            return;
        }

        const event: unknown = ev || {
            // Cannot use new Event() because event's target property is readonly
            target: document.querySelector(this.buttonSelector),
            stopPropagation: () => {}, // eslint-disable-line @typescript-eslint/no-empty-function
            preventDefault: () => {}, // eslint-disable-line @typescript-eslint/no-empty-function
        };
        this.popoverShown = true;

        this.popover = await CoreDomUtils.openPopoverWithoutResult({
            component: AddonModQuizConnectionErrorComponent,
            event: <Event> event,
        });

        this.popoverShown = false;
    }

    /**
     * Start a process to periodically check changes in answers.
     *
     * @param quiz Quiz.
     * @param attempt Attempt.
     * @param preflightData Preflight data.
     * @param offline Whether the quiz is being attempted in offline mode.
     */
    startCheckChangesProcess(
        quiz: AddonModQuizQuizWSData,
        attempt: AddonModQuizAttemptWSData,
        preflightData: Record<string, string>,
        offline?: boolean,
    ): void {
        if (this.checkChangesInterval || !quiz.autosaveperiod) {
            // We already have the interval in place or the quiz has autosave disabled.
            return;
        }

        this.previousAnswers = undefined;

        // Load initial answers in 2.5 seconds so the first check interval finds them already loaded.
        this.loadPreviousAnswersTimeout = window.setTimeout(() => {
            this.checkChanges(quiz, attempt, preflightData, offline);
        }, 2500);

        // Check changes every certain time.
        this.checkChangesInterval = window.setInterval(() => {
            this.checkChanges(quiz, attempt, preflightData, offline);
        }, this.CHECK_CHANGES_INTERVAL);
    }

    /**
     * Stops the periodical check for changes.
     */
    stopCheckChangesProcess(): void {
        clearTimeout(this.loadPreviousAnswersTimeout);
        clearInterval(this.checkChangesInterval);

        this.loadPreviousAnswersTimeout = undefined;
        this.checkChangesInterval = undefined;
    }

}